Prevention of magnesium burn-out in aluminum-magnesium alloys



United States Patent Pennsylvania N0 Drawing. Filed Apr. 9, 1965, Ser. No. 447,052 4 Claims. (Cl. 7568) This invention relates to aluminum-magnesium alloys and, more particularly, to prevention of burn-out of magnesium from aluminum base alloys containing upward of about 1% magnesium.

It is characteristic of aluminum-base alloys containing at least about 1% by weight of magnesium that this magnesium tends to burn at the surface of the alloy at the casting temperature. The resulting loss of magnesium alters the final composition of the cast alloy, and compensation must be made for an expendable amount of excess magnesium if burning is not avoided. It has been known for some time that the presence of a small quantity of beryllium in the molten aluminum-magnesium alloy effectively prevents magnesium burn-out, but when food containers are fabricated from the resulting alloy there is often fear of the toxicity of its beryllium content.

I have now discovered that cerium can be used in lieu of beryllium to prevent burn-out of magnesium from aluminum-magnesium alloys at alloying and casting temperatures. Pursuant to the present invention, the burn-out of magnesium added to molten aluminum in the production of an aluminum-base alloy containing at least 1% by weight of magnesium is prevented by incorporating in the molten aluminum an amount of cerium sufiicient to introduce between about 0.0001% and 0.1% by weigh-t of cerium into the molten aluminum. The cerium can be added as such, although it is presently preferred to add the cerium in the form of an aluminum-cerium master alloy.

In preparing the master alloy of aluminum and cerium, the cerium component can be obtained either from cerium metal or mischmetall. The lathanum component present in mischmetall has been found to be effective like cerium in preventing magnesium burn-out, and accordingly the term cerium herein and in the claims is to be interpreted as including lanthanum. In either case, the cerium-containing addition is sufficient to establish the desired cerium content in the aluminum-base master alloy. These master alloys have been made containing from 5% to 95% ccrium and from 12.5% to 60% mischmetall by weight of the aluminum component. All of these master alloy compositions were effective in preventing magnesium burnout in aluminum-magnesium alloys. The cerium or mischmetall is added directly to molten aluminum maintained at a temperature of about 1300" to 2400 F. while the surface of the molten aluminum is protected by a layer of any suitable flux or inert gas. The molten metal is stirred to assure homogeneity and is then cast into ingots.

The master alloy is effective in preventing burn-out of magnesium from aluminum-base alloys containing from about 1 /2% to about 12% by weight of magnesium. These aluminum-magnesium alloys are normally cast at temperatures within the range of 1100 to 1400 F., and at these temperatures there is no significant burn-out of their magnesium content when the master alloy of the invention has been added in an amount sufiicient to establish a cerium content of 0.0001% to 0.1% by weight, and preferably about 0.001%, in the aluminum-magnesium alloy. Larger amounts of cerium are useful in practicing the invention but are wasteful of cerium.

3,375,102 Patented Mar. 26, 1968 The effectiveness of cerium in preventing burn-out of magnesium is illustrated by the following tests. A magnesium-containing aluminum-base alloy, specifically a No. 220 alloy containing about 10% magnesium, was melted and maintained at various temperatures between 1950 and 25 00 F. These temperatures far exceeded the normal casting temperature for this alloy. Cerium was added to the aluminum-magnesium alloy batches in the form of aluminum-base master alloys containing 5% and 10% cerium and 12 /2% and 25% mischmetall. In each test, a fiame of burning magnesium was present at the surface of the molten aluminum-magnesium alloy before the cerium addition and this flame was promptly extinguished by additions of the aforemdntioned master alloys in amounts suflicient to establish a cerium content between 0.0008% and 0.07% by Weight in the aluminum-magnesium alloy. It will be readily appreciated that these tests were conducted under extremely severe temperature conditions and that they therefore establish the outstanding effectiveness of the practice of the invention in preventing magnesium burn-out in molten aluminum-magnesium a1 loys.

I claim:

1. The method of substantially preventing burn-out of magnesium added to molten aluminum in the production of an aluminum base alloy containing about 10% by weight of magnesium which comprises incorporating in the molten aluminum an amount of cerium sufficient to introduce between about 0.008% and 0.07% by weight of cerium into the molten aluminum.

2. The method of substantially preventing burn-out of magnesium added to molten aluminum in the production of an aluminum base alloy containing at least 1% by weight of magnesium which comprises incorporating in the molten aluminum an amount of cerium sufficient to introduce between about 0.0001% and 0.1% by weight of cerium into the molten aluminum.

3. The method of substantially preventing burn-out of magnesium added to molten aluminum in the production of an aluminum base alloy containing at least 1% by weight of magnesium which comprises incorporating in the molten aluminum a master alloy of aluminum and cerium in amount sufficient to introduce at least about 0.0001% by weight of cerium into the molten aluminum.

4. The method of substantially preventing burn-out of magnesium added to molten aluminum in the production of an aluminum base alloy containing at least 1% by weight of magnesium which comprises incorporating in the molten aluminum a master alloy of aluminum and cerium in amount suflicient to introduce between about 0.0001% and 0.1% by weight of cerium into the molten aluminum.

References Cited UNITED STATES PATENTS 2,336,512 12/1943 Stroup l47 3,236,632 2/ 1966 Foerster 75l47 X 3,252,841 5/1966 Foerster 75l47 X 3,278,300 10/1966 Koike 75l47 X FOREIGN PATENTS 417,106 9/ 1934 Great Britain.

597,308 l/ 1948 Great Britain.

621,617 4/ 1949 Great Britain.

DAVID L. RECK, Primary Examiner.

H. W. TARRING, Assistant Examiner. 

2. THE METHOD OF SUBSTANTIALLY PREVENTING BURN-OUT OF MAGNESIUM ADDED TO MOLTEN ALUMINUM IN THE PRODUCTION OF AN ALUMINUM BASE ALLOY CONTAINING AT LEAST 1% BY WEIGHT OF MAGNESIUM WHICH COMPRISES INCORPORATING IN THE MOLTEN ALUMINUM AN AMOUNT OF CERIUM SUFFICIENT TO INTRODUCE BETWEEN ABOUT 0.0001% AND 0.1% BY WEIGHT OF CERIUM INTO THE MOLTEN ALUMINUM. 